My gold sev is devloping dark scales??

I have a huge tank of American Cichlids, most are a dark colour but with the usual markings of their breed. However my gold severum has started to develope dark 'flicks' on his body and fins. I have a gold fish before that changed colour from balck to gold but this couldnt possibly happen in a Gold Sev. There is also and electric yellow in the tank so I ruled out him changing 'because he felt left out' (ive heard this happen before) and I have a Salvini as well. Im not thinking hes trying to mutate to comoflaugh either. However I may be wrong, it is diffcult to figure this one out. All the other fish are healthy.